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Development of e-textile at low cost wirelessly controlled Pulse Acquisition system and Vibration System for relaxing

Abstract— Nowadays Heart disease is one of the leading causes of mortality. Pulse determining devices plays an important role in measuring the current heart rate and can give a very well prediction about sudden heart problems. People mostly get tired at the end of the day and any middle of the day. If the pulse devices can be fabricated in jacket or with clothing in an inexpensive way then the system can automatically read the pulse and analyze the data with feedback about health condition.

So, this research is about developing a low cost, wireless e-textile with heart rate monitoring facility and body massaging facility through vibration for relaxing. Arduino Nano is used with Bluetooth module by that pulse can be monitored and controlled vibration in android app. This system is powered by battery, rechargeable and the system can be run for about 16 hours with continuous data acquisition.

Keywords—Heart rate, BPM, E-textile, Body massaging, IoT, Sensor.


A heart rate monitoring is a monitoring system that allows one to measure one’s heart rate in real-time or record the heart rate for later study [1]. A normal resting heart rate for adults’ ranges from 60 to 100 beats a minute [2].

Heart rate, or pulse, is the number of times heartbeats per minute. Normal heart rate varies from person to person. The best places to find your pulse are the wrists, inside of elbow, side of neck, top of the foot [3], [4].

Heart rate data can be really useful whether designing an exercise routine, studying activity or anxiety levels. The problem is that heart rate can be difficult to measure. It essentially combines a simple optical heart rate sensor [3] with amplification and noise cancellation circuitry making it fast and easy to get reliable pulse readings. It sips power with just 4mA current draw at 5V [3], [5].

Nowadays heart rate measuring instrument is available in smartphones, computers and portable devices. It will be very beneficial to the people if they get a wearable heart rate monitoring system with immediate feedback through IOT [6].

People generally want to get their medical feedback but it is not possible to go to the hospital. So, there is a solution to provide a heart rate monitoring in a wearable cloth by examining the blood flow at a low cost. Anyone can easily determine their health condition by determining the blood flow or BPM, especially the elder ones and patients of heart problems. It will be very attractive if there is an in-built body massaging system in that wearable textile [7].

The object of the research is to develop a low-cost heart rate monitoring system with body massaging facility, which is real-time [8], affordable, portable and user-friendly.

In this research

A prototype heart rate monitoring system is developed which is low cost, rechargeable battery-powered, portable and it includes the wireless facility for safety concern and reducing noise interference [5].

It gives wireless connectivity up to 10 meters. This designed system visualizes the bpm for the monitoring system and controls the vibration for body massage. It doesn’t detect abnormal bpm because of noise reduction algorithm [5].

An android app has been developed in which the data can be visualized and sent signal to start vibration [9].

The equipment used in this system consumes low power, for this reason, it can function for a long time.

There are seven pressure points in the back of the body which are targeted for making the prototype of the system [10]. Vibration modules have been planted in those pressure points of the inner back of the jacket for massaging the back of the subject as shown in figure 1.

Pressure Point for System
Figure 1: Selected Pressure Point for System.
  1. System architect

Modern Smartphones have more processing power and other features like Bluetooth (IEEE 802.15.1) [11], Wi-Fi (802.11) [12] and 4G.

Wi-Fi (802.11) [12] and 4G. Among smartphones, Android operating system is becoming popular nowadays and currently it dominates about 85% of world smartphone market. This makes it an attractive field to wirelessly monitor the heart rate as well as health and also can be controlled the vibration modules.

Arduino Nano is a low power and highly efficient microcontroller board based on the ATmega328P [13]. It has Fig. 1. Selected Pressure Point for Systembuilt in ADC and USART communication feature [13]. In this system, for analog to digital conversion and serial transmission of the pulse sensor data Arduino Nano is used.

System Architect of the e-textiles
Figure 2: System Architect of the e-textiles with wirelessly controlled pulse.
  1. Proposed methodology

This System is built through the microcontroller of Arduino Nano, Pulse sensor, relays and vibration modules. They are combined individually to get a better result.

  1. Vibration Module Unit: There is an off-centered weight attached to the motor’s rotational shaft that causes the motor to wobble [14]. The amount of wobble can be changed by the amount of weight that is attached, the weight’s distance from the shaft, and the speed at which the motor spins [14].

There is used protection layer to the outside of the motor so that the weight attached to the rotational shaft can move freely without any hamper. There is used glue gun to attach glue. One of the possible base materials of hot-melt adhesive is Ethylene-Vinyl acetate. Glue is not brittle but has elastic property so it will adjust with the subject. Then the module is soldered with solder iron and is attached to pass the electricity. In Figure 3 before and after adding glue layer is shown.

Preparing the Vibration Unit
Figure 3: Preparing the Vibration Unit.
  1. Pulse Acquisition Unit: The Pulse Sensor is actually a photo plethysmograph [15], which is popular as medical devices used for non-invasive heart rate monitoring. Usually, photo plethysmographs determine blood-oxygen levels (SpO2) but sometimes they don’t.

The heart pulse signal that comes out of a photo plethysmograph is an analog fluctuation in voltage [16], and it shows a predictable wave shape as shown in the figure. The depiction of the pulse wave is called a photo plethysmogram, or PPG [15].

This pulse sensor gives the raw data as well as amplify it for noise reduction in results and also normalizes the pulse of wave around midpoint in voltage which is V/2. Pulse Sensor Amped acts to relative changes in light intensity.

Light from the green LED that is reflected back to the sensor changes during each pulse. If the amount of light incident on the sensor remains constant, the signal value will remain at 512 or around 512. When more light comes the signal goes up. In times of less light, the opposite result occurs.

The code was developed to find successive moments of instantaneous heart beat and measure the time between, called the Inter Beat Interval (IBI) [17]. In figure 4 connection between microcontroller, pulse sensor and vibration module are shown.

Connection between Arduino, pulse sensor and vibration module
Figure 4: Connection between Arduino, pulse sensor and vibration module.
  1. Power Supply Unit: In this system two 3.7V disposable Lithium battery is used for making it portable. For safety and short circuit protection, a voltage regulator LM7805 [17] is used. In this system all equipment gets power from battery. It is done to avoid power line interference (50Hz) and other noise interference.

To recharge the power system there is added a charging IC and a protection circuit TP4056 [18]. In the figure 5 dual power supply for the system is shown.

Designed Dual Power Supply system
Figure 5: Designed Dual Power Supply for the system.
  1. ADC and Serial Transmission using Arduino Nano: Arduino Nano board contains an 8 channel 10-bit analog to digital converter. It returns a linear value from 0 to 1023 corresponding to 0V and +5V respectively [19].

For serial transmission baud rate is taken as 9600 bps and sampling rate of 320 samples per second is used. Arduino Nano has a built in USART communication feature which allow USART transmission and reception via digital pins 1 and 0 [19].

For serial communication pin 1 and pin 0 of Arduino Uno needs to connect with Bluetooth modules Rx and Tx and figure 6 shows the connections. A Bluetooth module HC-05 establishes signal transmission between Arduino UNO and Android phone. Arduino Uno can also communicate with laptop via USB cable.

Connection for Arduino Nano and Bluetooth Module HC-05
Figure 6 Connection for Arduino Nano and Bluetooth Module HC-05.
  1. Software implementation

There are two main parts of the software structure and they are device layer and application layer. The device layer is used to drive hardware and the application layer is for user to monitor pulse rate through BPM.

For programming the microcontroller, integrated development environment provided by the Arduino platform is used. An Android application and a software for laptop is developed by processing which is an open source programming language and integrated development environment IDE.

To develop the system there is used Processing IDE of version 2.21. For receiving serial data from Bluetooth module, BtSerial library was used [20]. For developing the software used in laptop serial library of processing was used to receive the data from Arduino Nano.

  1. Experimental measurements and results

We have connected all the circuits, electronic parts and sensors all together. This system can work together with laptop and smartphone or individually by using only smartphone or laptop. Android phone used for visualizing the data from the sensor and the phone has snapdragon-617 chipset and 2GB ram. In figure 8 heart rate is displayed both in the android phone and the laptop screen.

This system can work together with laptop and smartphone or individually by using only smartphone or laptop. The Laptop has Intel Core i5-6200U (2.4 GHz) processor and 8GB ram running on windows 10 OS. In laptop data is received by USB cable which is connected to Arduino UNO.

Pulse sensor added with fingertip
Figure 7: Pulse sensor added with fingertip.

Pulse sensor is tested on the subject of 22 years old. Data was taken from two positions of the body, one is fingertip and other is wrist of the hand. In the Figure 7 bpm of the fingertip is shown.

Experimental measurements performing both in Computer and android
Figure 8: Experimental measurements performing both in Computer and android.

Normally pulse gives noise without filtering. After filtering the pulse shows very low noise. In this research noise is minimized by adding noise reduction algorithm in the serial plotter of Arduino IDE.

Before noise reduction when in fingertip
Figure 9: Before noise reduction when in fingertip.
After noise reduction when in fingertip
Figure 10: After noise reduction when in fingertip.

In the figure 9 and figure 10, before and after noise reduction is shown in the case of fingertip.

From the above graph it is completely clear that signal without filtering, noise appears in BPM and to minimize noise, filtration is a must, and otherwise, the BPM cannot be measured properly.

In figure 11 and figure 12 before and after noise in the wrist of the hand is shown.

Before noise reduction when in Wrist of the hand
Figure 11: Before noise reduction when in Wrist of the hand.

In the figure 9-11 it can be noticed that each and every data is received and plotted in graph automatically by the software Arduino IDE 2.1.1 and before noise reduction, it can be easily determined that every data fluctuates from its previous data and after noise reduction the fluctuations are eliminated and are in range.

after noise reduction when in Wrist of the hand
Figure 12: after noise reduction when in Wrist of the hand.

The sensor values are transformed into the MATLAB Arduino serial communication and after data acquisition in MATLAB using the library, we get filtered PPG signal.

Filtered PPG signal from MATLAB
Figure 13: Filtered PPG signal from MATLAB.

By analyzing the data of both wrist of the left hand and the fingertip, noise is low in fingertip but to fabricate in the jacket we have to use wrist of any or left hand.

Testing of mi band 2 and the system developed
Figure 14: Testing of mi band 2 and the system developed.

In this research, data have been comparison between the developed system and between the mi band 2 available in the market which is certified and can be thought of standard. Both Fig. 10. After noise reduction when in fingertip developed system of this research and the mi band 2 in the market are comparison.

Table 1: Comparison of two different systems.
Developed System (BPM) Mi Band 2 (BPM) % Error
84 79 6.33%
83 85 2.4%
82 82 0%
86 89 3.5%
78 79 1.26%
82 74 10.8%
75 73 2.74%
82 80 2.5%
73 78 6.4%
86 85 1.18%
Average % Error 4.12%

In the table 1. Value of mi band 2 is set as true value and the value developed system is set as measured value. Then % error is calculated through the equation-

% error is calculated through the equation

The average error is about 4.12%. So, this can easily be accepted as a working prototype.

For testing vibration of the vibration module of the jacket we have used iDynamics app for measuring through the accelerometer sensor of the android phone. This testing is used in the Samsung Galaxy J7 (6) and the accelerometer sensor of the phone is K2HH Accelerometer. The maximum range of the accelerometer sensor is ±39.2266 m/s2.The accelerometer gives data in 3 axis-x axis,y axis, z axis.

accelerometer data for the x axis, y axis, z axis of acceleration
Figure 15: accelerometer data for the x axis, y axis, z axis of acceleration.

The measured value for vibration is determined from 3rd -21st sec because 0-3rd sec shows error.

accelerometer data for the x axis, y axis, z axis of velocity
Figure 16: accelerometer data for the x axis, y axis, z axis of velocity.

The more the RPM of the vibration module the more the vibration and as well as acceleration. The maximum value of acceleration, velocity and displacement is given on the below chart which is got from sensor data.

X-axis 25.592 1.0450 1.669
Y-axis 4.304 .20329 .2741
Z-axis 38.968 3.3695 5.12

By conversion the graph gives the value of 4-5 Hz. And human comfort zone and relaxation limits lies in .5-10 Hz range. The vibration module for relaxing works fine. The relative measure of the vibration is quite satisfying. Vibration unit of the system does not harm to anyone and it is in the comfort zone.

Bluetooth module (HC-05) that we used has a very little amount of radiation and it is too low to be considered dangerous to humans [21].

  1. Cost analysis

Table 2. shows the list of the component used for this system. Total cost of the system is USD 11.625.

Table 2. Cost of the equipment’s
Component Name Quantity Unit Price
Total Cost
Arduino NANO 1 1.875 1.875
HC-05 1 2.25 2.25
Resistor 6 0.01 .06
Capacitor 2 0.02 .04
Relay 1 0.8 0.8
Pulse Sensor 1 3.125 3.125
9V battery 1 1.10 1.10
TP4056 1 0.5 0.5
Vibration Module 7 0.25 1.75
Wire (yds) 2 .0625 .125
Total cost of the system 11.625
  1. Future development

In future, additional features can be added such as-ECG monitoring system, live tracking and alert system, Glucose level measurement, Blood pressure level measurement, live proximity alert system if anyone occurs any accident it will automatically reach out for help, adding washable property, increasing battery performance and fast charging property, fully IOT based system development etc.

  1. Conclusion

The main aim of this research is designing and building a low cost, wireless heart rate acquisition system has been fulfilled. As the system is wireless and battery powered, noise interference is reduced and subject safety is acquired.

This system is simple and effective for continuous pulse acquisition. The cost of the system is USD 11.625, which makes this system highly inexpensive and ideal for under developed and developing countries.

This system can be used in Android phone or can be monitored by any laptop. The component used for this system consumes very low power and the developed hardware for this system takes maximum current of 35 mA without using the vibration system. With vibration and the pulse sensor both draws current about 110 mA.

The system has been tested and found that it is capable of acquiring up to 16 hours of continuous heart rate data and during operation 25%of the CPU was utilized by the application. In future blood pressure level and blood sugar level recognition with updated feedback system can be added to this system.

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